Experimental investigation by Laser Ultrasonics for train wheelset flaw detection

Abstract

The transport safety is a key factor in the rail field and to ensure it the monitoring of train components structural integrity must be performed regularly and following strict regulations. Consequently, the development of Non-Destructive Testing (NDT) procedures is a topic of great interest and impact, it aiming at the early identification of cracks and inhomogeneities on train axle and wheels which propagation can causes faults and accidents undermining the passenger and crew safety. Ultrasound based nondestructive testing is currently applied in ordinary maintenance procedures, although they are applied to axle and wheels dismounted from the train wheelset. In fact, the technique requires ultrasonic probes to be in contact with the object under test and therefore the fretting surface between wheel and axle, where fatigue phenomenon induces cracks enucleation and propagation, cannot be monitored. The possibility of applying NDT systems to the whole wheelset, without dismounting it in its components, will allow drastically reducing the inspection time and increasing the inspection frequency. The present paper proposes a feasibility study for the development of a Laser-Ultrasonic Testing (LUT) procedure to improve performances of train wheelset ultrasonic inspection. The method exploits one or an array of air-coupled ultrasonic probes, which detects ultrasonic waves generated by a high-energy pulsed laser. Thanks to the non-contact nature of both the response measurement sensor and the excitation system, the experimental set-up is extremely flexible and it allows extremely speeding up the inspection time.